Transmission devices are employed in motorized vehicles to transfer torque from a torque generative device such as an internal combustion engine to a vehicle driveline for tractive effort in response to an operator request. Transmission devices include gear sets and clutches to transfer torque in one of a plurality of fixed gear ratios.
A shift from one gear element to another may be an upshift, i.e., a shift to a higher gear, or a downshift, i.e., a shift to a lower gear. The shift may be further defined as a power-on shift, i.e., a shift that occurs when an accelerator pedal is depressed, or a power-off shift, i.e., a shift that occurs when an accelerator pedal is released. Power-on shifts (upshifts and downshifts) may require more precise control than power-off shifts, as shifts that occur when a vehicle is accelerating may be more noticeable to a driver. Variation in clutch activation may occur between vehicles, and may also occur between shift events on a vehicle due to temperature, wear, and other factors. In one system, a variation in a clutch return spring rate of 5 kPa may effect clutch activation and an associated clutch shift feel. In present systems, developing a holding clutch ramp rate may require a time-intensive calibration effort.